From c80dd579e1d9c82fe2605e7252f98fb062ea9761 Mon Sep 17 00:00:00 2001
From: Zach Brown <zab@versity.com>
Date: Thu, 13 Jul 2017 08:56:06 -0700
Subject: [PATCH] scoutfs: add scoutfs_manifest_next_key

Add an item reading variant that just returns the next key that it finds
in segments after the given key.  This will be used while iterating
to find the next key to lock and then try to iterate towards.

Signed-off-by: Zach Brown <zab@versity.com>
---
 kmod/src/manifest.c | 35 +++++++++++++++++++++++++++++++----
 kmod/src/manifest.h |  3 +++
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/kmod/src/manifest.c b/kmod/src/manifest.c
index e8065724..6781f44e 100644
--- a/kmod/src/manifest.c
+++ b/kmod/src/manifest.c
@@ -542,6 +542,9 @@ out:
  * from the key to the end key.  If the end key is null then we'll read
  * as many items as the intersecting segments contain.
  *
+ * If next_key is provided then the segments are only walked to find the
+ * next key after the search key.  If none is found -ENOENT is returned.
+ *
  * As we insert the batch of items we give the item cache the range of
  * keys that contain these items.  This lets the cache return negative
  * cache lookups for missing items within the range.
@@ -559,9 +562,9 @@ out:
  * The segments are immutable at this point so we can use their contents
  * as long as we hold refs.
  */
-int scoutfs_manifest_read_items(struct super_block *sb,
-				struct scoutfs_key_buf *key,
-				struct scoutfs_key_buf *end)
+static int read_items(struct super_block *sb, struct scoutfs_key_buf *key,
+		      struct scoutfs_key_buf *end,
+		      struct scoutfs_key_buf *next_key)
 {
 	struct scoutfs_key_buf item_key;
 	struct scoutfs_key_buf found_key;
@@ -702,6 +705,16 @@ int scoutfs_manifest_read_items(struct super_block *sb,
 			found = true;
 		}
 
+		if (next_key) {
+			if (found) {
+				scoutfs_key_copy(next_key, &found_key);
+				ret = 0;
+			} else {
+				ret = -ENOENT;
+			}
+			break;
+		}
+
 		/* ran out of keys in segs, range extends to seg end */
 		if (!found) {
 			scoutfs_key_clone(&batch_end, &seg_end);
@@ -748,7 +761,7 @@ int scoutfs_manifest_read_items(struct super_block *sb,
 		ret = 0;
 	}
 
-	if (ret)
+	if (next_key || ret)
 		scoutfs_item_free_batch(sb, &batch);
 	else
 		ret = scoutfs_item_insert_batch(sb, &batch, key, &batch_end);
@@ -761,6 +774,20 @@ out:
 	return ret;
 }
 
+int scoutfs_manifest_read_items(struct super_block *sb,
+				struct scoutfs_key_buf *key,
+				struct scoutfs_key_buf *end)
+{
+	return read_items(sb, key, end, NULL);
+}
+
+int scoutfs_manifest_next_key(struct super_block *sb,
+			      struct scoutfs_key_buf *key,
+			      struct scoutfs_key_buf *next_key)
+{
+	return read_items(sb, key, NULL, next_key);
+}
+
 /*
  * Give the caller the segments that will be involved in the next
  * compaction.
diff --git a/kmod/src/manifest.h b/kmod/src/manifest.h
index 39e0e134..f36a58fe 100644
--- a/kmod/src/manifest.h
+++ b/kmod/src/manifest.h
@@ -34,6 +34,9 @@ int scoutfs_manifest_unlock(struct super_block *sb);
 int scoutfs_manifest_read_items(struct super_block *sb,
 				struct scoutfs_key_buf *key,
 				struct scoutfs_key_buf *end);
+int scoutfs_manifest_next_key(struct super_block *sb,
+			      struct scoutfs_key_buf *key,
+			      struct scoutfs_key_buf *next_key);
 
 int scoutfs_manifest_next_compact(struct super_block *sb, void *data);